In the previous grant period (12/01/83 - 12/31/85), we have established antigen-specific as well as nonspecific suppressor T cell hybridoma lines and characterized functional properties of their culture supernatant. The objectives of our current proposal are to obtain a highly purified, potent suppressor lymphokine(s) and to use it in vivo as a specific immunosuppressive reagent to induce allograft unresponsiveness. More specifically, the experiments described herein are designed 1) to further analyse physicochemical properties of the suppressor lymphokine with the use of various protein separation techniques; this study will provide information which is essential for the subsequent purification of highly potent, functionally defined suppressor lymphokine, 2) to investigate the mechanism(s) of suppression by binding studies and with the use of immune affinity chromatography, 3) to produce monoclonal antibodies reactive with the suppressor lymphokine, and 4) to establish optimal conditions for in vivo use of purified suppressor lymphokine in order to induce prolongation of allograft survival. We believe that the results obtained from these studies will provide important information for the establishment of better and more specific immunosuppressive therapy in clinical transplantation.